TW201436904A - Cu BALL - Google Patents

Abstract

Provided is a Cu ball having high sphericity and a low alpha dose despite containing at least given amounts of impurity elements besides Cu. Despite keeping the content of U and T to 5 ppb or less and purity at 99.995% or less in order to minimize soft errors and reduce connection defects, the alpha dose is 0.0200 cph/cm<SP>2</SP> or less. Unexpectedly, sphericity of the Cu ball was improved by keeping purity at 99.995% or less.

Description

Copper ball

The present invention relates to a copper ball having a small amount of alpha line.

In recent years, due to the development of small information devices, the electronic components mounted are rapidly miniaturizing. In order to reduce the size of the connection terminal and reduce the package area in response to the request for miniaturization, the electronic component is applied to a ball grid array (hereinafter referred to as "BGA") having an electrode provided on the back surface.

The electronic component to which the BGA is applied is, for example, a semiconductor component. In a semiconductor component, a semiconductor wafer having an electrode is sealed using a resin. The electrodes of the semiconductor wafer form solder bumps. The solder bumps are formed by bonding solder balls to the electrodes of the semiconductor wafer. A semiconductor component using a BGA is placed on a printed substrate by using each solder bump as a conductive land contacting the printed substrate, and heating and bonding the molten solder bump to the pad, It is mounted on a printed circuit board. Further, in order to meet the demand for further high-density packaging, a three-dimensional high-density package in which semiconductor components are stacked in the height direction is being studied.

However, when a BGA is applied to a semiconductor component that is packaged in a three-dimensional high-density package, the solder balls collapse due to the self-weight of the semiconductor component and a connection short-circuit occurs between the electrodes. This becomes a failure in high-density packaging.

Therefore, it is being studied to use a paste to bond copper balls to electronic parts. The electrode is made of solder bumps. A solder bump having a copper ball is when the electronic component is packaged on a printed substrate. Even if the weight of the semiconductor component plus the solder bumps, the semiconductor component can be supported by the copper ball which does not melt at the melting point of the solder. Thus, the solder bumps are not collapsed due to the self-weight of the semiconductor component. For the related art, for example, Patent Document 1 can be cited.

Although the miniaturization of electronic components can be packaged at a high density, high-density packaging has a problem of causing soft errors. The soft error refers to a possibility that the memory content is rewritten because the alpha line enters the memory cell of the semiconductor integrated circuit (hereinafter referred to as "IC"). It is considered that radioactive isotope such as U, Th, or ²¹⁰ Po (Polonium) in the α-line solder alloy is agglomerated and is emitted. Therefore, in recent years, development of a welding material having a low α line which reduces the content of radioactive ectopic elements has been carried out.

Therefore, it is required to reduce the soft error caused by the high-density packaging of the copper ball as described in Patent Document 1.

Prior technical literature Patent literature

[Patent Document 1] International Publication No. 95/24113

However, the alpha line system for copper balls has not been considered at all. Therefore, after the copper ball is welded, the α line is released by the diffusion of the radioactive element of the copper ball, and the problem that the soft line is caused by the α line of the copper ball being radiated into the memory cell of the semiconductor wafer has not been solved.

In this way, the α-line must be reduced in the solder joint portion of the copper ball. However, the amount of the α-line of the copper ball is included in Patent Document 1, and has not been studied in the past. It is considered that in the copper refining process, since the step of heating the copper to about 1000 ° C is performed, the radioactive isotope such as ²¹⁰ Po which emits the α line is volatilized, and the α line of copper is not a cause of soft error. Further, it is generally considered that when a copper ball is produced, the copper is heated to about 1000 ° C to be melted, and it is considered that the content of the radioactive isotope can be sufficiently reduced.

However, according to the manufacturing conditions of the previously produced copper ball, it cannot be proved that the α-line of the copper ball has been reduced to such an extent that no soft error is caused. ^{The 210} Po system has a boiling point of 962 ° C, and it is considered that the refining at about 1000 ° C can be sufficiently volatilized to such an extent that soft errors do not occur. However, because the previous copper refining, its purpose is not to make ²¹⁰ Po volatilize so, ²¹⁰ Po is not sufficiently reduce the temperature coefficient. According to the previous copper ball manufacturing, it is not clear whether a low-line copper ball system can be obtained.

Here, it is generally considered that a copper material having a high purity should be used to produce a copper ball, but the content of the element irrespective of the amount of the α-line of the copper ball is not necessarily reduced. Moreover, the use of excessively high purity copper will only increase the cost.

Further, when the copper ball system shows that the positive sphericity of the positive ball is low, when the solder bump is formed, the original function of the copper ball which controls the height of the standoff cannot be exhibited. Therefore, bumps having a non-uniform height are formed to cause problems in packaging. From the above background, a copper ball with a high degree of sphericity is desired.

An object of the present invention is to provide a copper ball having a high degree of sphericity, which has a small amount of α-line, even if it contains an impurity element other than a certain amount or more of copper.

The inventors of the present invention obtained the following knowledge: the purity of a commercially available copper material is 99.9 to 99.99% (hereinafter, 99% is set to 2N, 99.9% is set to 3N, 99.99% is set to 4N, and 99.999% is used. When it is set to 5N and 99.9999% is set to 6N), U and Th can be reduced to 5 ppb or less. In addition, the inventors of the present invention paid attention to the fact that although it is a soft error, it is impossible to quantitatively measure ²¹⁰ Po which is a small amount remaining in the content. Further, the inventors of the present invention obtained the following knowledge: heating the copper material in the production of the copper ball, or setting the temperature of the molten copper to be high, or heat-treating the granulated copper ball. In the case where the purity of the copper ball is 99.995% or less (hereinafter, 4 N5) or less, the α line amount of the copper ball can be suppressed to 0.0200 cph/cm ² or less.

Further, the inventors of the present invention have obtained the following knowledge: in order to increase the positive sphericity of the copper ball, the purity of the copper ball is 4 N5 or less, that is, an element other than copper contained in the copper ball (hereinafter, appropriately referred to as The "impurity element" is required to contain 50 ppm or more in total, and the present invention has been completed.

Here, the present invention is as follows.

(1) A copper ball characterized in that the total content of Pb and/or Bi is 1 ppm or more, the content of U is 5 ppb or less, the content of Th is 5 ppb or less, and the purity is 99.9% or more and 99.995% or less. The amount of the α line is 0.0200 cph/cm ² or less, and the positive sphericity is 0.95% or more.

(2) The copper ball according to (1) above, wherein the amount of the α line is 0.0020 cph/cm ² or less.

(3) The copper ball according to the above (1) or (2), wherein the amount of the α line is 0.0010 cph/cm ² or less.

(4) The copper ball according to any one of the above (1), wherein the diameter is from 1 to 1000 μm.

(5) A copper nucleus ball, comprising: the copper ball according to any one of the above (1) to (4); and solder plating coated with the copper ball.

(6) A copper nucleus ball, comprising: a copper ball according to any one of (1) to (4) above; a Ni (elickel plating) coated with the copper ball; The Ni-coated solder is plated with solder.

(7) A solder joint using the copper ball according to any one of the above (1) to (4).

(8) A solder joint using the copper core ball according to (5) or (6) above.

Fig. 1 is a SEM photograph of the copper ball of Example 1.

Fig. 2 is a SEM photograph of the copper ball of Example 2.

Fig. 3 is a SEM photograph of the copper ball of Comparative Example 1.

The present invention will be described in detail below. In the present specification, the unit (ppm, ppb, and %) of the composition of the copper ball is a ratio (mass ppm, mass ppb, and mass %) to the mass of the copper ball unless otherwise specified.

. U: 5 ppb or less, Th: 5 ppb or less

U and Th radioactive isotopes must be suppressed to suppress soft errors. In order to set the α line amount of the copper ball to 0.0200 cph/cm ² or less, the content of U and Th must be 5 ppb or less. Further, from the viewpoint of suppressing soft errors in current or future high-density packaging, the contents of U and Th are preferably 2 ppb or less.

. Copper ball purity: 99.995% or less

The copper ball system of the present invention has a purity of 4 N5 or less. That is, the content of the elemental element of the copper ball system of the present invention is 50 ppm or more. When the purity of the copper constituting the copper ball is within this range, a sufficient amount of crystal nucleus for increasing the positive sphericity of the copper ball can be secured in the molten copper. The reason why the positive sphericity is improved is as follows.

When a copper ball is produced, a copper material which forms a small piece of a predetermined shape is melted by heating, and the molten copper is spherical due to surface tension, and solidifies to form a copper ball. During the process of solidification of molten copper from a liquid state, crystal grains grow in spherical molten copper. In this case, when there are many impurities, the impurity element becomes a crystal nucleus and the growth of the crystal grain is suppressed. Therefore, the growth of the fine crystal grain system is suppressed, and the spherical molten copper system is a copper ball having a high degree of sphericity. On the other hand, when the amount of the impurity element is small, the crystal nucleus is relatively small, and the grain growth is not suppressed and grows with a certain orientation. As a result, a part of the spherical molten copper-based surface protrudes and solidifies. Such a copper ball system has a low true sphericity. As the impurity element, Sn, Sb, Bi, Zn, As, Ag, Cd, Ni, Pb, Au, P, S, U, Th, or the like can be considered.

The lower limit of the purity is not particularly limited, and is preferably 3 N or more from the viewpoint of suppressing the amount of α-line and suppressing deterioration of the conductivity and thermal conductivity of the copper ball due to a decrease in purity. That is, it is preferable that the content of the impurity element of the copper ball other than copper is 1000 ppm or less.

. α line amount: 0.0200 cph/cm ² or less

The α-line amount of the copper ball of the present invention is 0.0200 cph/cm ² or less. This is the amount of alpha line in the high-density packaging of electronic parts, where soft errors do not become a problem. In the present invention, the heat treatment is performed again in addition to the usual steps for producing a copper ball. Therefore, the ²¹⁰ Po system which is slightly residual in the copper material volatilizes, and the copper ball system shows a further lower α line amount than the copper material. From the viewpoint of suppressing soft errors in higher density packaging, the α line amount is preferably 0.0020 cph/cm ² or less, preferably 0.0010 cph/cm ² or less.

The preferred aspects are described below.

. The content of Pb and/or Bi is 1 ppm or more in total

As the impurity element, Sn, Sb, Bi, Zn, As, Ag, Cd, Ni, Pb, Au, P, S, U, Th, etc. can be considered, but among the copper ball system impurities of the present invention, special Pb The content of Bi and the total amount of Bi are preferably 1 ppm or more as an impurity element. In the present invention, in order to reduce the amount of α line, it is not necessary to reduce the content of Pb and/or Bi to the limit. This is based on the following reasons.

^{The 210} Pb and ²¹⁰ Bi systems change to ²¹⁰ Po due to β collapse. Therefore, in order to reduce the amount of α-line, it is generally considered that the content of Pb and/or Bi of the impurity element is also preferably as low as possible.

However, the ratios of ²¹⁰ Pb and ²¹⁰ Bi contained in Pb and Bi are relatively low. When the contents of Pb and Bi were considered to be reduced to some extent, the ²¹⁰ Pb and ²¹⁰ Bi systems were almost removed. The dissolution temperature of the copper of the copper ball of the present invention is set to be slightly higher than that of the prior art, or the copper material and/or the granulated copper ball are subjected to heat treatment. Although this temperature is lower than the boiling point of Pb or Bi, even if it is below the boiling point, the amount of the impurity element is reduced because of the gasification. Further, in order to increase the positive sphericity of the copper ball, the content of the impurity element is preferably higher. Therefore, the content of the copper ball system Pb and/or Bi of the present invention is preferably 1 ppm or more in total.

Moreover, in general, the content of Pb and/or Bi of the copper material is 1 ppm or more in total. Since the copper ball system of the present invention is as described above, since it is not necessary to remove ²¹⁰ Pb and ²¹⁰ Bi, it is not necessary to heat to a temperature higher than the boiling point of Pb and Bi. That is, the content of Pb and Bi is not greatly reduced. Thus, even if a certain amount of Pb and Bi remain after the production of the copper ball, the measurement error of the content is small. Therefore, Pb and Bi are important elements for estimating the content of the impurity element. From such a viewpoint, the content of Pb and/or Bi is preferably 1 ppm or more in total. The content of Pb and/or Bi is preferably 10 ppm or more in total. The upper limit is not particularly limited, and from the viewpoint of suppressing deterioration of conductivity of the copper ball, the content of Pb and/or Bi is preferably less than 1000 ppm in total.

. Positive sphericality of copper ball: 0.95 or more

The shape of the copper ball of the present invention is preferably 0.95 or more from the viewpoint of controlling the gap height, and when the positive spherical degree of the copper ball is less than 0.95, since the copper ball system has an indefinite shape, the bump is in the shape of the bump. When formed, bumps having a non-uniform height are formed, resulting in an increased possibility of causing joint failure. The positive sphericity system is preferably 0.990 or more. In the present invention, the positive sphericity system represents the offset from the positive sphere. The positive sphericity system can be obtained by various methods such as a least square center method (LSC method), a minimum area center method (MZC method), a maximum inward center method (MIC method), and a minimum external center method (MCC method).

. Copper ball diameter: 1~1000μm

The diameter of the copper ball of the present invention is preferably from 1 to 1000 μm. In this range, the spherical copper ball can be stably produced, and the connection short circuit when the terminals are narrowly spaced can be suppressed. Here, for example, the copper ball system of the present invention is used. In the case of paste, "copper ball" can also be called "copper powder". The "copper ball" is used in the case of "copper powder". Usually, the diameter of the copper ball is 1 to 300 μm.

An example of a method of producing a copper ball of the present invention will be described.

The copper material as the material is placed on a heat-resistant plate such as ceramic (hereinafter referred to as "heat-resistant plate"), and is heated in the furnace simultaneously with the heat-resistant plate. The bottom of the heat-resistant plate is provided with a plurality of circular grooves which are hemispherical. The diameter and depth of the groove can be appropriately set in accordance with the particle diameter of the copper ball, for example, a diameter of 0.8 mm and a depth of 0.88 mm. In addition, the copper-shaped copper material (hereinafter referred to as "grain material") obtained by cutting the copper thin wires is placed in a groove of the heat-resistant plate. A heat-resistant plate in which a crystal grain material is placed in a groove is heated in a furnace filled with an ammonia-decomposing gas to a temperature of 1100 to 1300 ° C and heat-treated for 30 to 60 minutes. At this time, when the furnace temperature is equal to or higher than the melting point of copper, the crystal grains are melted and become spherical. Subsequently, the inside of the furnace was cooled and the copper balls were formed in the grooves of the heat-resistant plate. After cooling, the formed copper ball is heat-treated again at 800 to 1000 ° C which is less than the melting point of copper.

Further, as another method, droplets of molten copper are dropped from an orifice provided at the bottom of the crucible, and the droplets are cooled to be granulated to form an atomization method of the copper spheres; the hot plasma cuts Cu A granulation method in which the metal is heated to a temperature above 1000 °C. The copper balls thus granulated may be reheated for 30 to 60 minutes at a temperature of 800 to 1000 ° C.

In the method for producing such a copper ball, the copper material may be heat-treated at 800 to 1000 ° C before granulation into a copper ball.

As the copper material which is a raw material of the copper ball, for example, a pellet, a thread, a column, or the like can be used. From the viewpoint of not excessively reducing the purity of the copper ball, the purity of the copper material can be 2N to 4N.

When such a high-purity copper material is used, the above-described heat treatment may not be performed, and the holding temperature of the molten copper may be lowered to about 1000 ° C in the same manner as before. As described above, the above-described heat treatment can be appropriately omitted and changed in accordance with the purity of the Cu material and the amount of α line. Further, when a copper ball having a high α-line amount and a copper ball having a different shape are produced, the copper balls can be reused as a raw material, and the amount of α-line can be reduced.

Moreover, the invention can also be applied to copper columns and copper columns.

Further, the copper ball of the present invention can also be applied to a so-called copper nucleus ball which is formed by applying various kinds of soldering on the surface using the copper ball of the present invention as a core. Further, after the Ni plating is applied to the surface of the copper ball, the copper core ball coated with the solder is coated to suppress the corrosion of the copper. Further, the copper ball and the copper core ball system of the present invention can be used for solder bonding of electronic parts.

[Examples]

Hereinafter, the embodiments of the present invention will be described, but the present invention is not limited thereto.

[Example 1]

Copper crystal grains having a purity of 3N (α-line amount: 0.0031 cph/cm ² , U: 1.5 ppb, Th: < 5 ppb) were placed in a crucible, and preheated at 900 ° C for 45 minutes. Subsequently, the temperature of the crucible was raised to 1200 ° C and heat treatment was performed for 45 minutes, and droplets of molten copper were dropped from the orifice provided at the bottom of the crucible, and the droplets were cooled to be granulated into a copper sphere. Thereby, a copper ball having an average particle diameter of 275 μm was produced. The elemental analysis results, the α line amount, and the positive sphericity of the produced copper balls are shown in Table 1. Hereinafter, a method of measuring the amount of α line and the degree of positive sphericity will be described in detail.

.线 line amount

Determination of the amount of α line

An alpha line measuring device using an air flow proportional counter. The measurement sample was a flat-bottomed container in which a copper ball was spread over 300 mm × 300 mm. The measurement sample was placed in an alpha line measuring device, and the amount of α line was measured using a PR-10 gas flow. Further, in the measurement of the PR-10 GAS (argon gas 90%-methane 10%), the PR-10 GAS was filled in a gas tank and passed for 3 weeks or more. The gas tank that has been used for more than 3 weeks is used in accordance with the alpha line measurement method specified by JEDEC (Joint Electron Device Engineering Council), and is not due to radon in the atmosphere. Entering the gas tank causes the alpha line to be generated.

. Positive sphericity

The positive sphericity is measured using a CNC image measuring system. The device is Ultra Quick Vision and ULTRA QV350-PRO manufactured by Mitutoyo Corporation.

Further, an SEM photograph of the produced copper ball is shown in Fig. 1. The magnification of the SEM photograph is 100 times.

[Embodiment 2]

A copper ball was measured in the same manner as in Example 1 except that a copper wire having a purity of 4 N5 or less (α line amount: 0.0026 cph/cm ² , U: <0.5 ppb or less, Th: <0.5 ppb) was used, and elemental analysis and α were measured. Line quantity. The results are shown in Table 1. Further, an SEM photograph of the copper ball produced in Example 2 is shown in Fig. 2 . The magnification of the SEM photograph is 100 times.

[Comparative Example 1]

A copper ball was measured in the same manner as in Example 1 except that a 6N copper plate having a purity higher than 4N5 (α line amount: <0.0010 cph/cm ² , U: 5 ppb or less, and Th: 5 ppb or less) was used, and elemental analysis and α were measured. Line quantity. The results are shown in Table 1. Further, an SEM photograph of the copper ball produced in Comparative Example 1 is shown in Fig. 3. The magnification of the SEM photograph is 100 times.

As shown in Table 1, although the purity of the copper balls of Examples 1 and 2 was 4 N5 or less and the content of Bi and Pb was 10 ppm or more, the α line amount was less than 0.0010 cph/cm ² . Further, since the purity of the copper ball system of Comparative Example 1 was higher than that of 4N5, the amount of α line was of course less than 0.0010 cph/cm ² . Further, the amount of α-line of the copper ball systems of Examples 1 and 2 was less than 0.0010 cph/cm ² for at least 4 years. Therefore, the copper balls of Examples 1 and 2 were also eliminated because of the recent problems in the increase in the amount of α line due to the change over time.

As shown in the first and second graphs, since the purity of the copper balls of Examples 1 and 2 is 4 N5 or less (the content of elements other than copper is 50 ppm or more), either of them shows a positive sphericity of 0.95% or more. . On the other hand, as shown in Fig. 3, the copper ball system of Comparative Example 1 has a higher purity than 4N5 (the content of elements other than copper is less than 50 ppm), so the positive sphericity is less than 0.95.

Claims (8)

A copper ball characterized in that the total content of Pb and/or Bi is 1 ppm or more, the content of U is 5 ppb or less, the content of Th is 5 ppb or less, and the purity is 99.9% or more and 99.995% or less, and the amount of α line is 0.0200 cph/cm ² or less, and the positive sphericity is 0.95% or more. The copper ball according to claim 1, wherein the amount of the α line is 0.0020 cph/cm ² or less. The copper ball according to claim 1 or 2, wherein the amount of the α line is 0.0010 cph/cm ² or less. The copper ball according to any one of claims 1 to 3, wherein the diameter is from 1 to 1000 μm. A copper nucleus ball comprising: a copper ball according to any one of claims 1 to 4; and a solder plating coated with the copper ball. A copper nucleus ball, comprising: a copper ball according to any one of claims 1 to 4; a Ni (elickel plating) coated with the copper ball; and the Ni plating Solder plating. A solder joint using a copper ball as described in any one of claims 1 to 4. A solder joint using a copper core ball as described in claim 5 or 6.